fix: make admin user deletion atomic and surface errors in UI

deleteUser() ran each child-table cleanup as a separate statement, so a
foreign-key violation on any step (e.g. sync_log rows from other users
referencing the deleted user's notes) would abort mid-way and leave the
database in a partial state. The API swallowed the error and the admin
page silently ignored the non-ok response, so clicking Delete and
confirming appeared to do nothing.

- Wrap the full cascade in a single sqlite transaction so the deletion
  is atomic.
- Also remove rows in sync_log, note_user_state, note_collaborators,
  note_versions, and attachments that belong to other users but
  reference the deleted user's notes, so the final DELETE FROM notes
  cannot trip a foreign-key check.
- Surface delete failures in the users settings UI instead of silently
  swallowing them.
- Add data-testids on the user row and delete button to support tests.
- Add e2e coverage for the admin user deletion flow (happy path,
  cancelled confirmation, and a user with notes / tags / attachments /
  preferences / api keys).

https://claude.ai/code/session_015T2HE6VzB64ZmSSyy1Wz4R

src/lib/server/auth.ts

@@ -227,29 +227,53 @@ export function getUser(userId: number): User | null {
 }
 
 export async function deleteUser(userId: number): Promise<void> {
-	// Cascade: delete user's data in dependency order
-	sqlite.prepare('DELETE FROM user_preferences WHERE user_id = ?').run(userId);
-	sqlite.prepare('DELETE FROM api_keys WHERE user_id = ?').run(userId);
-	sqlite.prepare('DELETE FROM note_user_state WHERE user_id = ?').run(userId);
-	sqlite
-		.prepare('DELETE FROM note_collaborators WHERE user_id = ? OR added_by = ?')
-		.run(userId, userId);
-	sqlite.prepare('DELETE FROM sync_log WHERE user_id = ?').run(userId);
-	sqlite.prepare('DELETE FROM attachments WHERE user_id = ?').run(userId);
-	sqlite
-		.prepare(
-			'DELETE FROM shared_notes WHERE note_id IN (SELECT id FROM notes WHERE user_id = ?)'
-		)
-		.run(userId);
-	sqlite
-		.prepare(
-			'DELETE FROM note_tags WHERE note_id IN (SELECT id FROM notes WHERE user_id = ?)'
-		)
-		.run(userId);
-	sqlite.prepare('DELETE FROM notes WHERE user_id = ?').run(userId);
-	sqlite.prepare('DELETE FROM tags WHERE user_id = ?').run(userId);
-	sqlite.prepare('DELETE FROM sessions WHERE user_id = ?').run(userId);
-	db.delete(users).where(eq(users.id, userId)).run();
+	// Atomic cascade: all-or-nothing. Also clear rows from other users that
+	// reference the deleted user's notes (e.g. sync_log, note_user_state,
+	// note_collaborators) so foreign-key checks don't block the final delete.
+	const tx = sqlite.transaction((uid: number) => {
+		sqlite.prepare('DELETE FROM user_preferences WHERE user_id = ?').run(uid);
+		sqlite.prepare('DELETE FROM api_keys WHERE user_id = ?').run(uid);
+		sqlite
+			.prepare(
+				'DELETE FROM note_user_state WHERE user_id = ? OR note_id IN (SELECT id FROM notes WHERE user_id = ?)'
+			)
+			.run(uid, uid);
+		sqlite
+			.prepare(
+				'DELETE FROM note_collaborators WHERE user_id = ? OR added_by = ? OR note_id IN (SELECT id FROM notes WHERE user_id = ?)'
+			)
+			.run(uid, uid, uid);
+		sqlite
+			.prepare(
+				'DELETE FROM sync_log WHERE user_id = ? OR note_id IN (SELECT id FROM notes WHERE user_id = ?)'
+			)
+			.run(uid, uid);
+		sqlite
+			.prepare(
+				'DELETE FROM attachments WHERE user_id = ? OR note_id IN (SELECT id FROM notes WHERE user_id = ?)'
+			)
+			.run(uid, uid);
+		sqlite
+			.prepare(
+				'DELETE FROM shared_notes WHERE note_id IN (SELECT id FROM notes WHERE user_id = ?)'
+			)
+			.run(uid);
+		sqlite
+			.prepare(
+				'DELETE FROM note_tags WHERE note_id IN (SELECT id FROM notes WHERE user_id = ?)'
+			)
+			.run(uid);
+		sqlite
+			.prepare(
+				'DELETE FROM note_versions WHERE note_id IN (SELECT id FROM notes WHERE user_id = ?)'
+			)
+			.run(uid);
+		sqlite.prepare('DELETE FROM notes WHERE user_id = ?').run(uid);
+		sqlite.prepare('DELETE FROM tags WHERE user_id = ?').run(uid);
+		sqlite.prepare('DELETE FROM sessions WHERE user_id = ?').run(uid);
+		sqlite.prepare('DELETE FROM users WHERE id = ?').run(uid);
+	});
+	tx(userId);
 }
 
 export async function changePassword(

src/routes/(app)/settings/users/+page.svelte

@@ -70,9 +70,16 @@
 			const res = await fetch(`/api/admin/users/${userId}`, { method: 'DELETE' });
 			if (res.ok) {
 				users = users.filter((u) => u.id !== userId);
+				createMsg = 'User deleted';
+				createError = false;
+			} else {
+				const d = await res.json().catch(() => ({}));
+				createMsg = d.message || 'Failed to delete user';
+				createError = true;
 			}
 		} catch {
-			// ignore
+			createMsg = 'Connection error';
+			createError = true;
 		}
 	}
 
@@ -167,7 +174,10 @@
 
 		<div class="space-y-3">
 			{#each users as user (user.id)}
-				<div class="flex flex-col gap-2 rounded-sm border border-[var(--border-subtle)] p-4 sm:flex-row sm:items-center sm:justify-between">
+				<div
+					class="flex flex-col gap-2 rounded-sm border border-[var(--border-subtle)] p-4 sm:flex-row sm:items-center sm:justify-between"
+					data-testid="user-row-{user.id}"
+				>
 					<div class="min-w-0">
 						<p class="truncate font-medium text-[var(--text)]">
 							{user.displayName || user.email}
@@ -195,6 +205,7 @@
 							</button>
 							<button
 								onclick={() => deleteUser(user.id)}
+								data-testid="delete-user-btn-{user.id}"
 								class="rounded-sm px-3 py-1 text-xs text-[var(--destructive)] hover:bg-[var(--error-bg)]"
 							>
 								Delete